1. Field
This relates generally to the manufacturing of semiconductor devices and, more specifically, to doping a non-planar semiconductor device.
2. Related Art
As semiconductor manufacturers continue to shrink the dimensions of transistor devices in order to achieve greater circuit density and higher performance, short-channel effects, such as parasitic capacitance and off-state leakage, increasingly impair transistor device characteristics. Fin field effect transistors (FinFETs), such as double-gate transistors, tri-gate transistors, and gate-all-around transistors, are a recent development in semiconductor processing for controlling such short-channel effects. A FinFET has a fin that protrudes above a substrate surface. The fin forms the body of the FinFET device and has fewer paths for current leakage than a planar body. Additionally, the fin creates a longer effective channel width, thereby increasing the on-state current and reducing short channel effects.
The fin defines the channel, the source/drain regions, and the source/drain extension regions of the FinFET. Like conventional planar metal-oxide semiconductor field effect transistors (MOSFETs), the channel, source, drain, source extension, and drain extension regions of a FinFET device are doped with impurities (i.e., dopants) to produce desired electrical characteristics. Ideally, these regions are each uniformly doped along the height of the fin. Poor dopant uniformity may cause undesirable threshold voltage variations across the height of the gate as well as source/drain punch-through issues.
One conventional method for doping the channel, source/drain, and source/drain extension regions of a FinFET is ion implantation. In order to provide uniform doping on both the top and sides of the fin, ion implantation is conventionally performed at a single energy and at an oblique angle to the vertical. However, as device structures become increasingly dense, adjacent structures, such as mask layers and neighboring fins, can cause implant shadowing and result in the non-uniform doping of the FinFET. One method for avoiding implant shadowing is to perform implants at a lower implant angle where dopants are implanted more vertically. However, a lower implant angle results in poor dopant distribution across the height of the fin as well as poor dopant retention along the sidewalls of the fin, thereby causing poor dopant uniformity in fin.